The present invention relates to a drive system for an electrochromic display containing an electrochromic material held in two electrode carrying support plates, at least one of which is transparent, to manifest reversible variations in the light absorption properties upon current supplied.
The present invention relates, more particularly, to a drive system which regenerates a memory state in an electrochromic display.
An electrochromic material is one in which the color is changed by the application of an electric field or current. See, for example, L. A. Goodman, "Passive Liquid Displays", RCA Report 613258.
There are two types of electrochromic displays (referred to as ECD hereinafter). The first type of ECD includes an inorganic solid film formed on electrodes, which produces color variations by the change in the opacity. The second type of ECD utilizes an electrically-induced chemical reduction of a colorless liquid to produce a colored, insoluble film on a cathode surface.
In such an ECD, memory effects are expected, which maintains the coloration state or the bleached state for several hours through several days as long as ECDs are held in an electrically opened state. However, the memory period is not infinite and, therefore, a colored display electrode is gradually bleached and/or a bleached display electrode is gradually colored when a certain display pattern is held for a period longer than the memory period of ECDs, for example, longer than ten (10) hours. This deteriorates the display quality.
Accordingly, an object of the present invention is to provide an improvement in a drive system for electrochromic displays which can enhance legibility of a visual display provided by the electrochromic displays.
Another object of the present invention is to regenerate a memory state in electrochromic displays.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, when a certain display pattern is desired to be maintained for a time period longer than the memory period of the ECD, all display electrodes are bleached by applying erase pulses and then desired display electrodes are again colored by applying write pulses. In another form, when a certain display pattern is desired to be maintained for a time period longer than the memory period of the ECD, erase pulses are applied to bleached display electrodes in an interval shorter than the memory period of the ECD.